RPC error response object violates JSON-RPC 2.0 specification

[jorisbontje]

http://www.jsonrpc.org/specification#error_object

5.1 Error object
When a rpc call encounters an error, the Response Object MUST contain the error member with a value that is a Object with the following members:

code
A Number that indicates the error type that occurred.
This MUST be an integer.
message
A String providing a short description of the error.
The message SHOULD be limited to a concise single sentence.
data
A Primitive or Structured value that contains additional information about the error.
This may be omitted.
The value of this member is defined by the Server (e.g. detailed error information, nested errors etc.).

However the RPC currently returns an object lacking the message and code attributes:

2015/02/03 10:20:21 [RPC] Sending payload: {"id":0,"jsonrpc":"2.0","error":true,"errortext":"Error: Could not parse request"}

[fjl]

@tgerring the standard library jsonrpc implementation handles this correctly.

[tgerring]

@fjl I'm not sure how we'd use the standard library to meet our needs in this case since the rpc package maps objects in the format of "Object.Method", differing from the style defined at https://github.com/ethereum/wiki/wiki/Generic-JSON-RPC

If it's possible, we can switch code over.

[fjl]

Damn. I thought there was a way around it. Nevermind then.

[tgerring]

Updates to JSON responses made in 55ed0ff

[jorisbontje]

Fixed